I can imagine and have experienced many kinds of trouble. Much of my planning includes avoiding troubles that never transpire. The ones in these verses are so unlikely that I do not bother planning for them. The earth giving way during an earthquake or volcano eruption, the mountains falling into the sea, and the waters roaring and foaming when a river goes over its banks, or the sea rushes inland during a tsunami have less chance of occurring than a bolt of lightning striking me.
Yet, that is the point; even if the most rare extreme trouble were to happen God is my refuge and strength, an ever-present help in trouble. Since this is true, then why do I fear? Fear in these cases is the result of a lack of trust in the love God has for me. “But God demonstrates his own love for us in this: While we were still sinners, Christ died for us.” (Romans 5:8)
So if the mountains look at me like they want to shake, or a summer storm threatens to give me a tsunami bath I can trust in God and not worry. I cannot add a single hour onto my life, as Jesus said, “by worrying.” (Matthew 6:27; Luke 12:25) So stop worrying and start acting like I am a loved child of God.